Rear projection screen having reduced scintillation

ABSTRACT

A rear projection screen of the present invention includes lens sheets or optical sheets having an optical function of condensing or diffusing light. The lens sheets or optical sheets have, as a whole, two or more diffusing layers (diffusing parts) separately provided in the light-transmitting direction. It is preferable that one of the two or more diffusing layers be provided on the light-entering-side surface of the outermost lens sheet or optical sheet on the light source side and that another one of the diffusing layers be provided on the light-emerging-side surface of the outermost lens sheet or optical sheet on the observation side. Any two of the two or more diffusing layers are such that the light-source-side diffusing layer has a diffusing power lower than that of the observation-side diffusing layer. Further, it is preferable that the types (refractive indexes or average particle diameters) of diffusers to be respectively incorporated into any two of the two or more diffusing layers be different from each other.

This is a continuation of application Ser. No. 09/029,848 filed Mar. 26,1998, now U.S. Pat. No. 6,271,965.

TECHNICAL FIELD

The present invention relates to rear projection screens chiefly usedfor rear-projection-type projectors such as video projectors and slideprojectors.

BACKGROUND ART

As rear projection screens of this type, there have conventionally beenknown those screens composed of a single lenticular lens sheetcomprising as a base material a synthetic resin such as polymethylmethacrylate, and those screens composed of such a lenticular lens sheetand other lens sheets. To form images on these rear projection screens,imaging light is projected on the screens by using light sources such asCRTs.

In recent years, projection tubes having small projection apertures,such as liquid crystal projectors and light bulbs came to be used aslight sources in place of CRTs. However, the conventional rearprojection screens have such a problem that, when images are formed onthese screens by the use of projection tubes having small projectionapertures, scintillation or speckle is caused on the images.

In order to solve this problem, there have conventionally been proposeda method in which the screens are scanned by using laser light sources(see Japanese Patent Laid-Open Publication No. 173094/1993); a method inwhich the screens are vibrated (see Reference 1 (J. Opt. Soc. Am., Vol.66, No. 11, Nov. 1976, “Speckle-free rear-projection screen using twoclose screens in slow relative motion”)); and a method in which largeamounts of diffusers are incorporated into lens sheets.

DISCLOSURE OF THE INVENTION

However, in the aforementioned conventional methods, the modification ofthe projectors themselves is needed, or additional apparatus arerequired in order to prevent images from undergoing scintillation or thelike. Further, the incorporation of large amounts of diffusers into lenssheets causes such troubles that the gain is decreased and that theresolution is unfavorably lowered.

The present invention was accomplished in view of the above-describeddrawbacks. An object of the present invention is therefore to provide arear projection screen capable of forming thereon an image free fromscintillation or the like with the decrease in gain and resolutionminimized without using any additional apparatus even when a projectiontube having a small projection aperture is used.

The first aspect of the present invention is a rear projection screencomprising a lens sheet having an optical function of condensing ordiffusing light, wherein the lens sheet has two or more diffusing partsseparately provided in a light-transmitting direction.

In the first aspect of the present invention, it is preferable that oneof the two or more diffusing parts be provided on a light-entering-sidesurface of the lens sheet and that another one of the diffusing parts beprovided on a light-emerging-side surface of the lens sheet. Further, itis preferable that the two or more diffusing parts be provided on asurface of the lens sheet and inside the same.

The second aspect of the present invention is a rear projection screencomprising two or more lens sheets or optical sheets having an opticalfunction of condensing or diffusing light, wherein at least one of thetwo or more lens sheets or optical sheets has at least one diffusingpart, and the two or more lens sheets or optical sheets have, as awhole, two or more diffusing parts.

In the second aspect of the present invention, it is preferable that thediffusing parts be provided on surfaces of the two or more lens sheetsor optical sheets, or inside the same. Further, it is preferable thatthe diffusing part of the outermost lens sheet or optical sheet on alight source side be provided on the light-entering-side surface of thislens sheet or optical sheet and that the diffusing part of the outermostlens sheet or optical sheet on an observation side be provided on alight-emerging-side surface of this lens sheet or optical sheet.

In the above-described first and second aspects of the presentinvention, any two of the two or more diffusing parts are preferablysuch that a light-source-side diffusing part has a diffusing power lowerthan that of an observation-side diffusing part. Further, any two of thetwo or more diffusing parts are preferably such that a light-source-sidediffusing part is formed by incorporating first diffusive fine particlesinto a first base material, that an observation-side diffusing part isformed by incorporating second diffusive fine particles into a secondbase material and that a difference between a refractive index of thefirst diffusive fine particles and that of the first base material issmaller than a difference between a refractive index of the seconddiffusive fine particles and that of the second base material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration showing a first embodiment of a rearprojection screen according to the present invention.

FIG. 2 is an illustration showing a second embodiment of a rearprojection screen according to the present invention.

FIG. 3 is an illustration showing a rear projection screen of Example 1according to the present invention.

FIG. 4 is an illustration showing a rear projection screen of Example 2according to the present invention.

FIG. 5 is an illustration showing a rear projection screen of Example 3according to the present invention.

FIG. 6 is an illustration showing a rear projection screen of Example 4according to the present invention.

FIG. 7 is an illustration showing a rear projection screen of Example 5according to the present invention.

FIG. 8 is an illustration showing a rear projection screen of Example 6according to the present invention.

FIGS. 9A and 9B are illustrations showing rear projection screens ofExample 7 according to the present invention.

FIG. 10 is an illustration showing a comparative rear projection screen.

BEST MODE FOR CARRYING OUT THE INVENTION

By referring now to the accompanying drawings, embodiments of thepresent invention will be described below.

First Embodiment

FIG. 1 is an illustration showing a first embodiment of a rearprojection screen according to the present invention.

As shown in FIG. 1, a rear projection screen 1 is composed of a singlelens sheet having on one surface or both surfaces thereof a Fresnel lensor lenticular lenses, wherein two or more diffusing parts 1A, 1B areprovided separately in the light-transmitting direction (in thedirection of the left and right sides in the figure). In this firstembodiment, the diffusing parts 1A and 1B are provided on thelight-entering-side surface (light-entering surface) andlight-emerging-side surface (light-emerging surface) of the lens sheet,respectively.

The diffusing parts 1A, 1B are parts for diffusing light, and canreadily be formed by a conventional method, for example, by using aresin layer containing a diffuser (diffusive fine particles) such asmicrolenses, glass beads or organic beads, or by embossing the surfacesof microlenses.

It is noted that the diffusing parts can be provided not only on thesurfaces of the lens sheet but also inside the lens sheet like adiffusing part 1C.

The diffusing parts 1A, 1B diffuse light emitted from a light source todestroy the coherence of the light, so that they can solve the problemof scintillation or speckle. However, when light from a light source isdiffused, the resolution is lowered. Further, when a large amount of adiffuser is incorporated into one diffusing part as in the conventionalmethod, the gain is decreased, and the image thus becomes very dark.

According to the first embodiment of the present invention, since thetwo diffusing parts 1A and 1B are separately provided on the lens sheet,it is possible to make the intensity of scintillation or the like low byusing a diffuser in an amount smaller than that of a diffuser which isrequired for a lens sheet having only one diffusing part to attain theequally low intensity of scintillation or the like. Moreover, since theamount of the diffuser used is small, the lowering of the gain isprevented, and the brightness of the image can thus be prevented frombeing unfavorably decreased.

Further, since the two diffusing parts 1A and 1B are separately providedon the lens sheet, it is enough to incorporate a decreased amount of adiffuser into one diffusing part. Therefore, the amount of stray lightto be produced inside the diffusing parts 1A, 1B can be decreased, andthe unfavorable lowering of resolution to be caused by flare, ghost orthe like can thus be prevented.

Furthermore, by this light-diffusing effect, moires to be formed by theinterference between Fresnel lenses, lenticular lenses, or pixels of alight source can be decreased.

It is preferable that the diffusing parts 1A and 1B be provided on thelight-entering-side surface and light-emerging-side surface of the lenssheet, respectively. The reason for this is as follows. When thediffusing parts 1A and 1B are provided at the above-described positions,the distance between the two diffusing parts becomes long, so that lightemitted from a light source cannot show coherence. Therefore, theintensity of scintillation or the like can be decreased, and thelowering of the brightness of the image can be minimized whilecontrolling the light-diffusing effect at the diffusing parts 1A and 1Bto extremely low.

Further, it is preferable that the diffusing power of the diffusing part1A on the light source side be made lower than that of the diffusingpart 1B on the observation side. By doing so, the degree of thediffusion of light which is caused on the light-entering side bydiffusing elements becomes low. The intensity of scintillation or thelike can thus be decreased while preventing the resolution from beingunfavorably lowered.

Scintillation or the like can be evaluated not only by theabove-described intensity of scintillation or the like, but also by themagnitude (roughness) of scintillation or the like which is caused whena dynamic picture image is projected. In order to decrease the intensityof scintillation or the like, it is preferable to use such a diffuserthat the difference between the refractive index of the diffuser andthat of a base material in which the diffuser is dispersed is small. Onthe other hand, in order to decrease the magnitude (roughness) ofscintillation or the like, it is preferable to use a diffuser whoseaverage particle diameter is small.

For this reason, when only scintillation or the like is taken intoconsideration, it seems to be effective to incorporate, into both thediffusing part 1A on the light source side and the diffusing part 1B onthe observation side, a diffuser whose average particle diameter issmall and whose refractive index is such that the difference between therefractive index of the diffuser and that of a base material in whichthe diffuser is dispersed is small. However, a diffuser whose refractiveindex is such that the difference between the refractive index of thediffuser and that of a base material in which the diffuser is dispersedis small, or a diffuser whose average particle diameter is small makesthe angle of visibility narrow. Therefore, in order to solve the problemof scintillation or the like and that of the angle of visibility at thesame time, it is preferable that the type of a diffuser to beincorporated into the diffusing part 1A be made different from that of adiffuser to be incorporated into the diffusing part 1B.

Specifically, as will be described later in Example 7, it is preferablethat the difference between the refractive index of a diffuser to beincorporated into the diffusing part 1A on the light source side andthat of a base material in which the diffuser is dispersed be madesmaller than the difference between the refractive index of a diffuserto be incorporated into the diffusing part 1B on the observation sideand that of a base material in which the diffuser is dispersed, and thata diffuser having an average particle diameter not greater than apredetermined size (e.g., 15 micrometers) be incorporated into thediffusing part 1B on the observation side.

A variety of methods have been known as the method for controlling thedegree of the diffusion of light. Specifically, when a diffusing part isformed by means of embossing, irregularities to be produced by embossingare changed; and when a diffuser is employed, the particle diameter,refractive index, or amount of the diffuser to be used is changed. Therelationship between the particle diameter, refractive index or the likeof a diffuser and the light-diffusing effect is described in, forexample, Reference 2 (J. Opt. Soc. Am. A, Vol. 2, No. 12, Dec. 1985,“Diffraction analysis of bulk diffusers for projection-screenapplications”).

Second Embodiment

FIG. 2 is an illustration showing a second embodiment of a rearprojection screen according to the present invention.

As shown in FIG. 2, a rear projection screen 2 is composed of two ormore lens sheets or optical sheets 2-1, 2-2, 2-3, . . . , and diffusingparts 2A, 2B, 2C, . . . are provided on the lens sheets or opticalsheets 2-1, 2-2, 2-3, . . . , respectively.

In this figure, the diffusing part 2A is provided on thelight-entering-side surface (light-entering surface) of the outermostlens sheet or optical sheet 2-1 on the light source side; the diffusingpart 2B is provided on the light-emerging-side surface (light-emergingsurface) of the outermost lens sheet or optical sheet 2-2 on theobservation side; and the diffusing part 2C is provided on thelight-entering-side surface (light-entering surface) of the lens sheetor optical sheet 2-3.

As the lens sheet for use in this embodiment, it is possible to employ alinear or circular Fresnel lens sheet, a lenticular lens sheet having onone surface or both surfaces thereof lenticular lenses, a lens sheethaving on each surface thereof a combination of Fresnel lenses orlenticular lenses, or the like.

As the optical sheet, a panel made from polymethyl methacrylate or thelike, whose both surfaces are flat, or the like can be used.

The properties of the diffusing parts 2A, 2B, 2C, . . . , and theproperties related to the configuration of the diffusing parts 2A, 2B.2C, . . . , are the same as those of the diffusing parts 1A, 1B, 1C inthe above-described first embodiment. Therefore, detailed explanationsfor these properties are herein omitted.

EXAMPLES

Specific examples of the rear projection screens as shown in FIGS. 1 and2 will be given below.

Example 1

FIG. 3 is an illustration showing a rear projection screen of Example 1according to the present invention. Example 1 corresponds to the firstembodiment shown in FIG. 1, and, in this rear projection screen ofExample 1, two diffusing layers (diffusing parts) are separatelyprovided on both surfaces of a single lens sheet.

Namely, in this Example, a rear projection screen 10 was produced, asshown in FIG. 3, by respectively providing diffusing layers 10A and 10Bon the light-entering surface 11 a and light-emerging surface 11 b of alens sheet 11 made from polymethyl methacrylate, having a thickness of 5mm. The diffusing layer 10A was formed on the light-entering surface 11a by embossing a Fresnel lens part on the light-entering surface 11 a.On the light-emerging surface 11 b of the lens sheet 11 was formed thediffusing layer 10B having a thickness of 500 micrometers, in which 15parts by weight of glass beads having an average particle diameter of 11micrometers and a refractive index of 1.535 were dispersed. It is notedthat, in this Example and also in the following Examples 2 to 7 andComparative Example, the amount (parts by weight) of the diffuser suchas glass beads is a value based on 100 parts by weight of the basematerial into which the diffuser is incorporated.

As the base material of the lens sheet 11, an impact-resistantmethacrylic resin (refractive index 1.51) manufactured by SumitomoChemical Co., Ltd., Japan was used. As the glass beads having an averageparticle diameter of 11 micrometers and a refractive index of 1.535,“EMB20” manufactured by Toshiba-Ballotini Co., Ltd., Japan was used.

An image was projected on the thus-produced rear projection screen 10 byusing an LCD projector, and observed for evaluation. As a result, it wasconfirmed that the intensity of scintillation caused on the image waslow and that the resolution of the image was excellent.

Example 2

FIG. 4 is an illustration showing a rear projection screen of Example 2according to the present invention. Example 2 corresponds to the secondembodiment shown in FIG. 2, and, in this rear projection screen ofExample 2, two diffusing layers (diffusing parts) are separatelyprovided on two lens sheets, one diffusing part on one lens sheet. Oneof the two diffusing layers is provided on the surface of the lens sheet(the light-entering-surface of a Fresnel lens sheet).

Namely, in this Example, a rear projection screen 20 was produced, asshown in FIG. 4, by the combination use of a Fresnel lens sheet 21having a thickness of 2 mm, made from polymethyl methacrylate, and alenticular lens sheet 22 having a thickness of 1 mm, made frompolymethyl methacrylate. On the light-entering surface 21 a of theFresnel lens sheet 21 was formed a diffusing layer 20A having athickness of 150 micrometers, in which 7.0 parts by weight of organicbeads (cross-linked polymer beads) having an average particle diameterof 12 micrometers and a refractive index of 1.59 were dispersed.Further, into the lenticular lens sheet 22 (diffusing layer 20B) werehomogeneously incorporated 0.75 parts by weight of organic beads havingan average particle diameter of 12 micrometers and a refractive index of1.59.

As the base material of the Fresnel lens sheet 21 and that of thelenticular lens sheet 22, an impact-resistant methacrylic resin(refractive index 1.51) manufactured by Sumitomo Chemical Co., Ltd.,Japan was used. As the organic beads having an average particle diameterof 12 micrometers and a refractive index of 1.59, “PB3011” (styrenebeads) manufactured by Sumitomo Chemical Co., Ltd., Japan was used.

An image was projected on the thus-produced rear projection screen 20 byusing an LCD projector, and observed for evaluation. As a result, it wasconfirmed that the intensity of scintillation caused on the image waslow and that the resolution of the image was excellent.

Example 3

FIG. 5 is an illustration showing a rear projection screen of Example 3according to the present invention. Example 3 corresponds to the secondembodiment shown in FIG. 2, and, in this rear projection screen ofExample 3, two diffusing layers (diffusing parts) are separatelyprovided on three lens/optical sheets. One of the two diffusing layersis provided on the surface of the outermost lens sheet on the lightsource side (the light-entering-surface of a Fresnel lens sheet), andthe other diffusing layer is provided on the surface of the outermostoptical sheet on the observation side (the light-entering-surface of aflat face panel).

Namely, in this Example, a rear projection screen 30 was produced, asshown in FIG. 5, by the combination use of a Fresnel lens sheet 31having a thickness of 2 mm, made from polymethyl methacrylate, a flatface panel 32 having a thickness of 2 mm, made from polymethylmethacrylate, and a lenticular lens sheet 33 having a thickness of 1 mm,made from polymethyl methacrylate, containing no diffuser, providedbetween the Fresnel lens sheet 31 and the flat face panel 32. On thelight-entering surface 31 a of the Fresnel lens sheet 31 was formed adiffusing layer 30A having a thickness of 150 micrometers, in which 45parts by weight of glass beads having an average particle diameter of 11micrometers and a refractive index of 1.535 were dispersed. On thelight-entering surface 32 a of the flat face panel 32 was formed adiffusing layer 30B having a thickness of 150 micrometers, in which 45parts by weight of glass beads having an average particle diameter of 11micrometers and a refractive index of 1.535 were dispersed.

As the base materials of the Fresnel lens sheet 31, of the flat facepanel 32 and of the lenticular lens sheet 33, an impact-resistantmethacrylic resin (refractive index 1.51) manufactured by SumitomoChemical Co., Ltd., Japan was used. As the glass beads having an averageparticle diameter of 11 micrometers and a refractive index of 1.535,“EMB20” manufactured by Toshiba-Ballotini Co., Ltd., Japan was used.

An image was projected on the thus-produced rear projection screen 30 byusing an LCD projector, and observed for evaluation. As a result, it wasconfirmed that the intensity of scintillation caused on the image waslow and that the resolution of the image was excellent.

Example 4

FIG. 6 is an illustration showing a rear projection screen of Example 4according to the present invention. Example 4 corresponds to the secondembodiment shown in FIG. 2, and, in this rear projection screen ofExample 4, two diffusing layers (diffusing parts) are separatelyprovided on two lens sheets. One of the two diffusing layers is providedon the surface of the outermost lens sheet on the light source side (thelight-entering-surface of a Fresnel lens sheet), and the other diffusinglayer is provided inside the outermost lens sheet on the observationside (inside a lenticular lens sheet). Further, the diffusing layerprovided on the light source side has a diffusing power lower than thatof the diffusing layer provided on the observation side.

Namely, in this Example, a rear projection screen 40 was produced, asshown in FIG. 6, by the combination use of a Fresnel lens sheet 41having a thickness of 2 mm, made from polymethyl methacrylate, and alenticular lens sheet 42 obtained by forming transparent lenses 42 b onboth surfaces of a film 42 a having a thickness of 200 micrometers, madefrom polymethyl methacrylate. On the light-entering surface 41 a of theFresnel lens sheet 41 was formed a diffusing layer 40A having athickness of 100 micrometers, in which 35 parts by weight of glass beadshaving an average particle diameter of 11 micrometers and a refractiveindex of 1.535 were dispersed. Further, into the film 42 a (diffusinglayer 40B) of the lenticular lens sheet 42 were homogeneouslyincorporated 10.0 parts by weight of organic beads having an averageparticle diameter of 12 micrometers and a refractive index of 1.59.

As the base material of the Fresnel lens sheet 41, an impact-resistantmethacrylic resin (refractive index 1.51) manufactured by SumitomoChemical Co., Ltd., Japan was used. As the glass beads having an averageparticle diameter of 11 micrometers and a refractive index of 1.535,“EMB20” manufactured by Toshiba-Ballotini Co., Ltd., Japan was used.Further, as the organic beads having an average particle diameter of 12micrometers and a refractive index of 1.59, “PB3011” (styrene beads)manufactured by Sumitomo Chemical Co., Ltd., Japan was used. Thelenticular lens sheet 42 was obtained by covering, with the film 42 a, aUV- (ultraviolet-) or EB- (electron beam-) curable resin poured into amold in a shape reverse to the shape of the transparent lenses 42 b, andapplying ultraviolet rays or electron beams to the UV- or EB-curableresin.

An image was projected on the thus-produced rear projection screen 40 byusing an LCD projector, and observed for evaluation. As a result, it wasconfirmed that the intensity of scintillation caused on the image waslow and that the resolution of the image was excellent.

Example 5

FIG. 7 is an illustration showing a rear projection screen of Example 5according to the present invention. Example 5 corresponds to the secondembodiment shown in FIG. 2, and, in this rear projection screen ofExample 5, two diffusing layers (diffusing parts) are separatelyprovided on two lens sheets. One of the two diffusing layers is providedon the surface of the outermost lens sheet on the light source side (thelight-entering-surface of a Fresnel lens sheet), and the other diffusinglayer is provided on the surface of the outermost lens sheet on theobservation side (the light-emerging surface of a lenticular lenssheet). Further, the diffusing layer provided on the light source sidehas a diffusing power lower than that of the diffusing layer provided onthe observation side.

Namely, in this Example, a rear projection screen 50 was produced, asshown in FIG. 7, by the combination use of a Fresnel lens sheet 51having a thickness of 2 mm, made from polymethyl methacrylate, and alenticular lens sheet 52 having a thickness of 1 mm, made frompolymethyl methacrylate. On the light-entering surface 51 a of theFresnel lens sheet 51 was formed a diffusing layer 50A having athickness of 100 micrometers, in which 35 parts by weight of glass beadshaving an average particle diameter of 11 micrometers and a refractiveindex of 1.535 were dispersed. On the light-emerging surface 52 b of thelenticular lens sheet 52 was formed a diffusing layer 50B having athickness of 100 micrometers, in which 12.0 parts by weight of organicbeads having an average particle diameter of 12 micrometers and arefractive index of 1.59 were dispersed.

As the base material of the Fresnel lens sheet 51, and that of thelenticular lens sheet 52, an impact-resistant methacrylic resin(refractive index 1.51) manufactured by Sumitomo Chemical Co., Ltd.,Japan was used. As the glass beads having an average particle diameterof 11 micrometers and a refractive index of 1.535, “EMB20” manufacturedby Toshiba- Ballotini Co., Ltd., Japan was used. Further, as the organicbeads having an average particle diameter of 12 micrometers and arefractive index of 1.59, “PB3011” (styrene beads) manufactured bySumitomo Chemical Co., Ltd., Japan was used.

An image was projected on the thus-produced rear projection screen 50 byusing an LCD projector, and observed for evaluation. As a result, it wasconfirmed that the intensity of scintillation caused on the image waslow and that the resolution of the image was excellent.

Example 6

FIG. 8 is an illustration showing a rear projection screen of Example 6according to the present invention. Example 6 corresponds to the secondembodiment shown in FIG. 2, and, in this rear projection screen ofExample 6, three diffusing layers (diffusing parts) are separatelyprovided on three lens/optical sheets, one diffusing layer on one lensor optical sheet. The three diffusing layers are respectively providedon the surfaces (the light-entering surfaces) of the three lens/opticalsheets.

Namely, in this Example, a rear projection screen 60 was produced, asshown in FIG. 8, by the combination use of a Fresnel lens sheet 61having a thickness of 2 mm, made from polymethyl methacrylate, a flatface panel having a thickness of 2 mm, made from polymethylmethacrylate, and a lenticular lens sheet 63 having a thickness of 1 mm,made from polymethyl methacrylate, provided between the Fresnel lenssheet 61 and the flat face panel 62. On the light-entering surface 61 aof the Fresnel lens sheet 61 was formed a diffusing layer 60A having athickness of 100 micrometers, in which 3.5 parts by weight of glassbeads having an average particle diameter of 11 micrometers and arefractive index of 1.535 were dispersed. On the light-entering surface62 a of the flat face panel 62 was formed a diffusing layer 60B having athickness of 100 micrometers, in which 3.5 parts by weight of glassbeads having an average particle diameter of 11 micrometers and arefractive index of 1.535 were dispersed. On the light-entering surface63 a of the lenticular lens sheet 63 was formed a diffusing layer 60Chaving a thickness of 300 micrometers, in which 5.0 parts by weight oforganic beads having an average particle diameter of 30 micrometers anda refractive index of 1.49 were dispersed.

As the base materials of the Fresnel lens sheet 61, of the flat facepanel 62, and of the lenticular lens sheet 63, an impact-resistantmethacrylic resin (refractive index 1.51) manufactured by SumitomoChemical Co., Ltd., Japan was used. As the glass beads having an averageparticle diameter of 11 micrometers and a refractive index of 1.535,“EMB20” manufactured by Toshiba-Ballotini Co., Ltd., Japan was used.Further, as the organic beads having an average particle diameter of 30micrometers and a refractive index of 1.49, “XC01” (acrylic beads)manufactured by Sumitomo Chemical Co., Ltd., Japan was used.

An image was projected on the thus-produced rear projection screen 60 byusing an LCD projector, and observed for evaluation. As a result, it wasconfirmed that the intensity of scintillation caused on the image waslow and that the resolution of the image was excellent.

Example 7

FIGS. 9A and 9B are illustrations showing rear projection screens ofExample 7 according to the present invention. Example 7 corresponds tothe second embodiment shown in FIG. 2, and, in these rear projectionscreens of Example 7, two diffusing layers (diffusing parts) areseparately provided on two lens sheets. Further, the type (refractiveindex and average particle diameter) of the diffuser incorporated intothe diffusing layer provided on the light source side is different fromthat of the diffuser incorporated into the diffusing layer provided onthe observation side.

Namely, in this Example, rear projection screens 70, 80 were produced,as shown in FIGS. 9A and 9B, by the combination use of Fresnel lenssheets 71, 81 made from polymethyl methacrylate, and lenticular lenssheets 72, 82 having a thickness of 1 mm, made from polymethylmethacrylate. As shown in FIGS. 9A and 9B, the shape and structure ofthe rear projection screen 70 are identical with those of the rearprojection screen 80 except that the structure of the Fresnel lens sheet71 is different from that of the Fresnel lens sheet 81.

As the base material of the Fresnel lens sheets 71, 81, animpact-resistant methacrylic resin (refractive index 1.51) manufacturedby Sumitomo Chemical Co., Ltd., Japan was used. This resin was subjectedinto extrusion molding, and a Fresnel lens part was formed on onesurface of the molded product by coating thereto a UV-curable resincontaining no diffuser, followed by curing the UV-curable resin by theapplication of ultraviolet rays, thereby obtaining the Fresnel lenssheets 71, 81. It is noted that the boundary between the substrate andthe Fresnel lens part formed thereon by the use of the UV-curable resinis not shown in FIGS. 9A and 9B.

The Fresnel lens sheet 71 shown in FIG. 9A is a lens sheet obtained byforming a Fresnel lens part on one surface of a single layer (diffusinglayer 70A), serving as a substrate, into which a diffuser having apredetermined average particle diameter and refractive index ishomogeneously incorporated. On the other hand, the Fresnel lens sheet 81shown in FIG. 9B is a lens sheet obtained by forming a Fresnel lens parton one surface of a co-extruded two-layered substrate having, on thelight-entering surface 81 a thereof, a diffusing layer 80A in which adiffuser having a predetermined average particle diameter and refractiveindex is dispersed.

Into the diffusing layers 70A, 80A was incorporated, as the diffuser,one of (1) acrylic beads having an average particle diameter of 30micrometers and a refractive index of 1.49 (“XC01” manufactured bySumitomo Chemical Co., Ltd., Japan), (2) acrylic beads having an averageparticle diameter of 11 micrometers and a refractive index of 1.49(“MBX” manufactured by Sekisui Chemical Co., Ltd., Japan), (3) glassbeads having an average particle diameter of 17 micrometers and arefractive index of 1.535 (“EGB210” manufactured by Toshiba-BallotiniCo., Ltd., Japan), and (4) styrene beads having an average particlediameter of 12 micrometers and a refractive index of 1.59 (“PB3011”manufactured by Sumitomo Chemical Co., Ltd., Japan).

These diffusers (1) to (4) were incorporated into the diffusing layers70A, 80A of the Fresnel lens sheets 71, 81 in a manner as shown in thefollowing Table 1.

TABLE 1 Concentration of Diffuser Thickness of on Light- on ObservationDiffusing Layer Entering Side Side (mm) XC01 2.5t  2.0P — XC01 1.8t 3.0P — XC01 1.8t (2)  17P Clear 0.2 MBX 1.8t 1.15P — MBX 1.8t (2) 9.0PClear 0.2 EGB 1.8t (2) 6.8P Clear 0.2 EGB 2.5t (2) 3.4P Clear 0.4 PB30111.8t 0.17P —

In the above Table 1, the numeral (e.g. “2.5 t”) shown next to the typeof the diffuser (e.g., “XC01”) indicates the thickness (mm) of thesubstrate of the Fresnel lens sheet 71, 81. The thickness of the Fresnellens sheet 71, 81 is the sum total of the thickness of the substrate and0.2 mm, the thickness of the Fresnel lens part formed by using aUV-curable resin. Further, the numeral in parentheses, “(2)”, shown nextto the numeral (e.g., “1.8 t”) indicating the thickness (mm) of thesubstrate represents that the substrate of the Fresnel lens sheet intowhich the diffuser is incorporated has a two-layered structure (thestructure as shown in FIG. 9B). The unit (P) of the concentration of thediffuser is parts by weight (number of grams) of the diffuserincorporated into 100 parts by weight (100 g) of polymethylmethacrylate, the base material.

On the other hand, as the base material of the lenticular lens sheets72, 82, an impact-resistant methacrylic resin (refractive index 1.51)manufactured by Sumitomo Chemical Co., Ltd., Japan was used as in thecase of the above-described Fresnel lens sheets 71, 81. The entirelenticular lens sheets 72, 82 were obtained by subjecting the resin toextrusion molding. As shown in FIGS. 9A and 9B, diffusing layers 70B,80B having a thickness of 600 micrometers, in which a diffuser having apredetermined particle diameter and refractive index was dispersed wererespectively formed on the light-emerging surfaces of the lenticularlens sheets 72, 82.

Into the diffusing layers 70B, 80B was incorporated, as the diffuser,one of (1) glass beads having an average particle diameter of 11micrometers and a refractive index of 1.535 (“EMB20” manufactured byToshiba-Ballotini Co., Ltd., Japan), (2) glass beads having an averageparticle diameter of 17 micrometers and a refractive index of 1.535(“EGB210” manufactured by Toshiba-Balliotini Co., Ltd., Japan), (3) a6:1 mixture of acrylic beads having an average particle diameter of 30micrometers and a refractive index of 1.49 (“XC01” manufactured bySumitomo Chemical Co., Ltd., Japan) and the above “EGB210” manufacturedby Toshiba-Ballotini Co., Ltd., Japan (XC01+EGB-1), and (4) a 2:3mixture of the above “XC01” manufactured by Sumitomo Chemical Co., Ltd.,Japan and the above “EGB210” manufactured by Toshiba-Ballotini Co.,Ltd., Japan (XC01+EGB-2).

These diffusers (1) and (4) were incorporated into the diffusing layers70B, 80B of the lenticular lens sheets 72, 82 in the following manner.Namely, among the above-described diffusers (1) and (4), the diffuser(3), which is a 6:1 mixture of “XC01” manufactured by Sumitomo ChemicalCo., Ltd., Japan and “EGB210” manufactured by Toshiba-Ballotini Co.,Ltd., Japan, “XC01+EGB-1”, was taken as a standard, and theconcentration of the “EG210” contained in the “XC01+EGB-1” was made 2.0P. The concentrations of the other diffusers (1), (2) and (4) were soadjusted that the gain of a rear projection screen obtainable by thecombination use of a lenticular lens sheet containing the diffuser (1),(2) or (4), and the Fresnel lens sheet having the diffusing layerindicated by “XC01 2.5 t” in the above Table 1 would be almost equal(within±0.2) to the gain of a rear projection screen obtainable by thecombination use of the lenticular lens sheet having the diffusing layercontaining the above-described diffuser “XC01+EGB-1”, and theabove-described Fresnel lens sheet having the diffusing layer indicatedby “XC01 2.5 t”.

Rear projection screens 70, 80 were respectively produced by assembling,in a frame (not shown in the figure), the above-described variousFresnel lens sheets 71, 81 and lenticular lens sheets 72, 82. Whiteimages were projected on the thus-produced various rear projectionscreens 70, 80 by using an LCD projector, and evaluated in terms of theintensity and magnitude (roughness) of scintillation or the like causedon the images. The results obtained are as shown in the following Table2. The magnitude (roughness) of scintillation or the like was evaluatedby the roughness of speckle perceived by an observer when he/she movedhis/her eyes. The intensity and magnitude (roughness) of scintillationor the like were evaluated according to 6 ranks of “5” (most excellent)to “0” (poorest).

TABLE 2 XC01 + EGB-1 XC01 + EGB-2 EGB EMB magnitude magnitude magnitudemagnitude intensity (roughness) intensity (roughness) intensity(roughness) intensity (roughness) XC01 2.5t 5 4 5 4 5 4 5 5 XC01 1.8t 32 3 2 2 2 2 3 XC01 1.8(2) 4 4 4 4 3 4 5 5 MBX 1.8t 3 2 3 2 2 2 2 3 MBX1.8t(2) 4 4 4 4 3 4 5 5 EGB 1.8t(2) 3 2 2 2 2 2 2 4 EGB 2.5t(2) 4 4 3 43 4 3 4 PB3011 1.8t 1 1 1 0 0 0 0 1 XC01: acrylic beads (30 μm, 1.49)EMB: glass beads: (11 μm, 1.535) MBX: acrylic beads (11 μm, 1.49) XC01 +EGB-1: a 6:1 mixture of “XC01” and “EGB” EGB: glass beads: (17 μm,1.535) XC01 + EGB-2: a 2:3 mixture of “XC01” and “EGB” PB3011: styrenebeads (12 μm, 1.59)

The results shown in the above Table 2 demonstrate that those screensproduced by using acrylic beads having an average particle diameter of30 micrometers and a refractive index of 1.49 (“XC01” manufactured bySumitomo Chemical Co., Ltd., Japan) as the diffuser to be incorporatedinto the Fresnel lens sheet (FL) on the light source side, and glassbeads having an average particle diameter of 11 micrometers and arefractive index of 1.535 (“EMB20” manufactured by Toshiba-BallotiniCo., Ltd., Japan) as the diffuser to be incorporated into the lenticularlens sheet (LL) on the observation side show good results in terms ofboth the intensity and magnitude (roughness) of scintillation or thelike.

Further, from the results shown in the above Table 2, the followingtendency is confirmed: the intensity of the scintillation or the likebecomes lower and the magnitude (roughness) of the same becomes smalleras the difference between the refractive index of the diffuser to beincorporated into the Fresnel lens sheet (FL) on the light source sideand that (1.51) of the base material in which the diffuser is dispersedbecomes smaller (for instance, compare the “MBX 1.8 t” series resultswith the “PB3011 1.8 t” series results, where the average particlediameter of “MBX” is almost equal to that of “PB3011”). Furthermore, itis also confirmed that the magnitude (roughness) of scintillation or thelike becomes smaller as the average particle diameter of the diffuserincorporated into the lenticular lens sheet (LL) on the observation sidebecomes smaller (for instance, compare the “EGB” series results with the“EMB” series results, where the refractive index of “EGB” is equal tothat of “EMB”). With respect to the average particle diameter of thediffuser to be incorporated into the lenticular lens sheet (LL), a greatimprovement is found in the magnitude (roughness) of scintillationbetween the average particle diameter of 17 micrometers (“EGB210”) andthat of 11 micrometers (“EMB20”), especially in the vicinity of theaverage particle diameter of 15 micrometers.

The following is also confirmed from the results shown in the aboveTable 2: the intensity of scintillation becomes lower and the magnitude(roughness) of the same becomes smaller as the thickness of the Fresnellens sheet (FL) becomes greater, and when the Fresnel lens sheet is notcomposed of a single layer but composed of two layers.

Comparative Example

FIG. 10 is an illustration showing a comparative rear projection screen.

In this Comparative Example, a rear projection screen 70 was produced,as shown in FIG. 10, by the combination use of a Fresnel lens sheet 91having a thickness of 2 mm, made from polymethyl methacrylate.containing no diffuser, and a lenticular lens sheet 92 having athickness of 1 mm, made from polymethyl methacrylate. Into thelenticular lens sheet 72 (diffusing layer 90B), 5 parts by weight ofglass beads having an average particle diameter of 11 micrometers and arefractive index of 1.535 were homogeneously incorporated.

As the base material of the Fresnel lens sheet 91, and that of thelenticular lens sheet 92, an impact-resistant methacrylic resin(refractive index 1.51) manufactured by Sumitomo Chemical Co., Ltd.,Japan was used. As the glass beads having an average particle diameterof 11 micrometers and a refractive index of 1.535, “EMB20” manufacturedby Toshiba-Ballotini Co., Ltd., Japan was used.

An image was projected on the thus-produced rear projection screen 90 byusing an LCD projector, and observed for evaluation. As a result, it wasconfirmed that the intensity of scintillation caused on the image washigh and that the quality of the image was poor.

According to the present invention, since at least two diffusing partsare separately provided on one lens sheet or optical sheet, or on aplurality of lens sheets or optical sheets, it is possible to make theintensity of scintillation low by using a diffuser in an amount smallerthan that of a diffuser which is required for a lens sheet having onlyone diffusing part to attain tile equally low intensity ofscintillation. Further, by respectively incorporating diffusers ofdifferent types into two diffusing parts, not only the intensity ofscintillation or the like can be made low, but also the magnitude(roughness) of the same can be made small. Scintillation or the like tobe caused on an image can thus be effectively decreased without loweringthe resolution and brightness of the image.

What is claimed is:
 1. A rear projection screen comprising: a lens sheetfor condensing or diffusing light, said lens sheet comprising aplurality of diffusing parts spaced from each other in alight-transmitting direction by a non-diffusing part, wherein two of thediffusing parts comprise a light-source side diffusing part and anobservation-side diffusing part, the light-source side diffusing parthaving a diffusing power lower than the diffusing power of theobservation-side diffusing part, the light-source side diffusing partbeing formed by incorporating first diffusive fine particles into afirst base material, and the observation-side diffusing part beingformed by incorporating second diffusive fine particles into a secondbase material, a refractive index difference between the first diffusivefine particles and the first base material being smaller than arefractive index difference between the second diffusive fine particlesand the second base material.
 2. The rear projection screen according toclaim 1, wherein one of the two or more diffusing parts is provided on alight-entering-side surface of the lens sheet, and another one of thediffusing parts is provided on a light-emerging-side surface of the lenssheet.
 3. The rear projection screen according to claim 1, wherein thetwo or more diffusing parts are provided on a surface of the lens sheetand inside the same.
 4. The rear projection screen according to claim 1,wherein the second diffusive fine particles have an average particlediameter not greater than 15 micrometers.
 5. A rear projection screencomprising: a plurality of lens sheets or optical sheets for condensingor diffusing light, at least one of said lens sheets or optical sheetscomprising at least one diffusing part so that said lens sheets oroptical sheets, as a whole, comprise a plurality of diffusing partsspaced from each other in a light-transmitting direction by anon-diffusing part, wherein two of the diffusing parts comprise alight-source side diffusing part and an observation-side diffusing part,the light-side diffusing part having a diffusing power lower than thediffusing power of the observation-side diffusing part, the light-sidediffusing part being formed by incorporating first diffusive fineparticles into a first base material, and the observation-side diffusingpart being formed by incorporating second diffusive fine particles intoa second base material, a refractive index difference between the firstdiffusive fine particles and the first base material being smaller thana refractive index difference between the second diffusive fineparticles and the second base material.
 6. The rear projection screenaccording to claim 5, wherein the diffusing parts are provided onsurfaces of the two or more lens sheets or optical sheets, or inside thesame.
 7. The rear projection screen according to claim 5, wherein thediffusing part of the outermost lens sheet or optical sheet on a lightsource side is provided on a light-entering-side surface of this lenssheet or optical sheet, and the diffusing part of the outermost lenssheet or optical sheet on an observation side is provided on alight-emerging-side surface of this lens sheet or optical sheet.
 8. Therear projection screen according to claim 5, wherein the seconddiffusive fine particles have an average particle diameter not greaterthan 15 micrometers.